package com.annotationAndReflection;


import java.lang.annotation.*;
import java.lang.reflect.Field;

//通过反射操作注解
//以数据库表的映射结构为例
public class TestReflectionOperationNotes {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName("com.annotationAndReflection.Student2");

        //通过反射获得注解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);//@com.annotationAndReflection.MyTable(value=db_student)
        }
        //获得注解value的值
        MyTable myTable = (MyTable)c1.getAnnotation(MyTable.class);
        String value = myTable.value();
        System.out.println(value);//db_student

        //获得类指定的注解
        Field f = c1.getDeclaredField("name");//"id","age"
        MyField annotation = f.getAnnotation(MyField.class);
        System.out.println(annotation.columnName());//db_name
        System.out.println(annotation.type());//varchar
        System.out.println(annotation.length());//30
    }

}

@MyTable("db_student")
class Student2{
    @MyField(columnName = "db_id",type = "int",length = 10)
    private int id;
    @MyField(columnName = "db_age",type = "int",length = 10)
    private int age;
    @MyField(columnName = "db_name",type = "varchar",length = 30)
    private String name;

    public Student2() {
    }

    public Student2(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student2{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}

//类名的注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface MyTable{
    String value();//需要参数:数据库名
}

//属性的注解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface MyField{
    //设置三个参数
    String columnName();
    String type();
    int length();
}
    